Piston choice is often more the question here.

For rough, rutted surfaces, it is recommended to run a larger/fewer hole piston and slightly thicker oil. This allows the shock to work quickly on the "chatter" type bumps, getting the wheel back to the ground quicker and not "pack up" on compression.

The down side to larger hole pistons is that they do not "pack up" as much as more or smaller hole pistons. If the track has a jump that shoots you high, with no downside landing, a smaller hole with more holes piston works better here, providing more high shaft speed damping (pack) when flat landing a jump, keeping the chassis from bottoming out (the dreaded "chassis slap").

VRP or Vision Racing Products has come out with an effective manner to provide the best of both worlds with their Game Changer pistons. The GC pistons have both dynamic compression and rebound valves. On rough, rutted surfaces, you can get the suppleness needed to keep the wheels on the ground for maximum traction. The additional rebound flaps/holes help get the wheel back down to the surface quicker. The Carbon Fiber Compression Valves actuate at fast shock shaft speeds, as in the example of flat landing a jump. The CFCV closes a few holes, helping the shock pack up, only when needed.

I've been running the GC pistons for a little over a year now, with great success. I'm constantly comparing them to the latest, trend build of shocks for my car. I keep a second set of shocks with the preferred pistons, springs, oil and build type (emulsion in this case) in my box. I have yet to find the standard piston setup better than the GC shocks, across the multiple tracks that I race at.

Lastly, I've tried the GC piston shocks with both emulsion and bladder builds. The best lap times and handling were achieved with a bladder build, using vented caps, custom drilled (extra 1.5mm vent hole) with maybe 25% rebound. I also test between the legacy and new low frequency springs that Tekno offers. Again, best lap times and performance were with the legacy springs.

1/8th scale, 4WD vehicles have a lot to consider for optimizing performance. Break it down, testing specific features to learn what works best for you.

Best advice that I've followed: if I make a change and it does NOT show a noticeable improvement, undo that change. Even if the change appeared to have NO effect, undo it. If you don't, you can eventually make so many changes away from your original setup, that the car becomes undriveable.